Chemical Bonding and Nomenclature

1. Chemical Bonding and Nomenclature Chapter 5

2. What is a Molecule ? • Molecule • A collection of atoms bonded together • Elemental molecules • Atoms from same element • Diatomic: H2, N2, O2, F2, I2, Br2 • Polyatomic: P4, S8

3. What is a Molecule • Molecules of Compounds • Atoms of different elements • Simple vs. Complicated • Small vs. extremely large

4. Properties of Molecules • Molecules have different properties than their elemental component.

5. Properties of Molecules

6. Why do molecules form? • To be like the noble gases • The noble gases are perfect hence they do not react with anything • They have 8 valence electrons in their outer most shell

7. Valence Electrons? • The outermost electrons. Determines the chemical properties of an element • The only electrons that bond • The roman numerals at the top of each group A element • Most elements prefer to have 8 electrons this is called the octet rule. Why?

8. The Octet Rule Atoms tend to gain, lose, or share electrons until they have eight valence electrons.

9. Electron Dot diagrams • A way of keeping track of valence electrons. • How to write them • Write the symbol. • Put one dot for each valence electron • Don’t pair up until you have too. X

10. The Electron Dot diagram for Nitrogen • Nitrogen has 5 valence electrons. • First we write the symbol. N • Then add 1 electron at a time to each side. • Until they are forced to pair up.

11. Write the electron dot diagram for • Na • Mg • C • O • F • Al • He

12. Electron Configurations for Cations • Metals lose electrons to attain noble gas configuration. • They make positive ions.

13. Electron Dots For Cations • Metals will have few valence electrons Ca

14. Electron Dots For Cations • Metals will have few valence electrons • These will come off Ca

15. Electron Dots For Cations • Metals will have few valence electrons • These will come off • Forming positive ions Ca+2

16. Electron Configurations for Anions • Nonmetals gain electrons to attain noble gas configuration. • They make negative ions.

17. Electron Dots For Anions • Nonmetals will have many valence .electrons. • They will gain electrons to fill outer shell. P P-3

18. Stable Electron Configurations • All atoms react to achieve noble gas configuration. • Noble gases 8 valence electrons . • Also called the octet rule. Ar

19. Covalent Bonding

20. + + How does H2 form? • The nuclei repel

21. + + How does H2 form? • The nuclei repel • But they are attracted to electrons • They share the electrons

22. Covalent bonds • Nonmetals hold onto their valence electrons. • They can’t give away electrons to bond. • Still want noble gas configuration. • Get it by sharing valence electrons with each other. • By sharing both atoms get to count the electrons toward noble gas configuration.

23. F Covalent bonding • Fluorine has seven valence electrons

24. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven

25. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons

26. Single Covalent Bond • A sharing of two valence electrons. • Only nonmetals and Hydrogen.

27. How to show how they formed • It’s like a jigsaw puzzle. • I have to tell you what the final formula is. • You put the pieces together to end up with the right formula. • For example- show how water is formed with covalent bonds.

28. H O Water Each hydrogen has 1 valence electron Each hydrogen wants 1 more The oxygen has 6 valence electrons The oxygen wants 2 more They share to make each other happy

29. O Water • Put the pieces together • The first hydrogen is happy • The oxygen still wants one more H

30. O Water • The second hydrogen attaches • Every atom has full energy levels H H

31. Multiple Bonds • Sometimes atoms share more than one pair of valence electrons. • A double bond is when atoms share two pair (4) of electrons. • A triple bond is when atoms share three pair (6) of electrons.

32. O Carbon dioxide • CO2- Carbon is central atom( I have to tell you) • Carbon has 4 valence electrons • Wants 4 more • Oxygen has 6 valence electrons • Wants 2 more C

33. O Carbon dioxide • Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short C

34. O O Carbon dioxide • Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short C

35. O O Carbon dioxide • The only solution is to share more C

36. O O Carbon dioxide • The only solution is to share more C

37. O Carbon dioxide • The only solution is to share more O C

38. O Carbon dioxide • The only solution is to share more O C

39. O Carbon dioxide • The only solution is to share more O C

40. Carbon dioxide • The only solution is to share more O C O

41. Carbon dioxide • The only solution is to share more • Requires two double bonds • Each atom gets to count all the atoms in the bond O C O

42. Carbon dioxide • The only solution is to share more • Requires two double bonds • Each atom gets to count all the atoms in the bond 8 valence electrons O C O

43. Carbon dioxide • The only solution is to share more • Requires two double bonds • Each atom gets to count all the atoms in the bond 8 valence electrons O C O

44. Carbon dioxide • The only solution is to share more • Requires two double bonds • Each atom gets to count all the atoms in the bond 8 valence electrons O C O

45. F F F S F F F F B F F H O H N O Very unstable!! A. Octet Rule • Exceptions: • Hydrogen  2 valence e- • Groups 1,2,3 get 2,4,6 valence e- • Expanded octet  more than 8 valence e- (e.g. S, P, Xe) • Radicals  odd # of valence e-

46. B. Drawing Lewis Diagrams • Find total # of valence e-. • Arrange atoms - singular atom is usually in the middle. • Form bonds between atoms (2 e-). • Distribute remaining e- to give each atom an octet (recall exceptions). • If there aren’t enough e- to go around, form double or triple bonds.

47. B. Drawing Lewis Diagrams • CF4 1 C × 4e- = 4e- 4 F × 7e- = 28e- 32e- F F C F F - 8e- 24e-

48. B. Drawing Lewis Diagrams • BeCl2 1 Be × 2e- = 2e- 2 Cl × 7e- = 14e- 16e- ClBeCl - 4e- 12e-

49. B. Drawing Lewis Diagrams • CO2 1 C × 4e- = 4e- 2 O × 6e- = 12e- 16e- OCO - 4e- 12e-

50. C. Polyatomic Ions • To find total # of valence e-: • Add 1e- for each negative charge. • Subtract 1e- for each positive charge. • Place brackets around the ion and label the charge.